In many contexts, it is desirable to be able to localise a spot within an object and, for example, to guide and insert an instrument to exact position in the spot. This is of particular importance in breast cancer diagnosis using int. al. fine-needle biopsy which may be considered as included in the clinical and cytological components in triple diagnostics. This triple diagnostics procedure generally includes mammography, clinical examination and cytology. Fine-needle biopsy or fine needle puncture with cytological examination of cell samples from a suspected region provide very reliable positive responses. Furthermore, it is desirable, using fine-needle biopsy, to be able to indicate a spot by means of a thin wire marker for facilitating subsequent surgical excision biopsy.